Heretofore, determination of endotoxin with a limulus amebocyte lysate has been known. This method is based on coagulation of lysate with a very small amount of endotoxin, for example at about 10.sup.-9 g. It has been elucidated with the progress of biochemistry that this coagulation reaction consists of the stepwise activation mechanism of some coagulation factors. (Takanori Nakamura et al., Jpn. J. Bacteriol., 38, 781-803 (1983)). FIG. 1 shows the coagulation cascade reaction of Japanese horseshoe crab (Tachypleus tridentatus). The structures of three serine protease precursors (factor C, factor B and proclotting enzyme) and a clottable protein (coagulogen) in FIG. 1 have been elucidated by studies such as cDNA cloning (i. Muta et al. (1991) J. Biol. Chem., 265, 22426-22433 and 266, 6554-6561, and T. Miyata et al (1986) J. Biochem., 100, 213-220).
The lysate has been known to react with (1.fwdarw.3)-.beta.-D-glucan which exists in the cell walls of fungi and yeasts, at concentrations of 10.sup.-8 -10-9 g to trigger coagulation (see FIG. 1). Factor G responds to (1.fwdarw.3)-.beta.-D-glucans, initiating clot formation. It is reported that factor G is a serine protease precursor as well as the other factors and it is a glycoprotein composed of non-covalently associated subunits a (72 kDa) and b (37 kDa) (64th Annual Meeting of Japan Biochemical Society, 1991).
Additionally, subunit a of factor G has a specific binding site to (1.fwdarw.3)-.beta.-D-glucan and subunit b has serine protease region. Factor G is supposed to be activated and express serine protease activity by the binding of (1.fwdarw.3)-.beta.-D-glucan to subunit a. However, the complete structure of factor G remains unknown.